docs: def clean_text(self, email, **kwargs):
          """Parse and normalize an email address.
  
          Returns None if this is not an email address.
          """
          if not self.EMAIL_REGEX.match(email):
              return None
          email = strip_quotes(email)
          mailbox, domain = email.rsplit('@', 1)
          domain = self.domains.clean(domain, **kwargs)
          if domain is None or mailbox is None:
              return
          return '@'.join((mailbox, domain))